BECAUSE THEY CAN LOWER THE PRICE OF ALL LABELED COMPOUNDS, IMPROVED METHODS FOR THE SYNTHESIS OF 13C AND 15N-LABELED PRECURSORS REMAINS AN IMPORTANT ACTIVITY FOR THE SIR STAFF. OVER THE PAST SEVERAL YEARS WE HAVE RECOGNIZED THE NEED TO IMPROVE THEISOTOPIC YIELD OF [1,2-13C2]ACETYLENE FROM 13CO2. ACETYLENE IS PRODUCED BY THE HYDROLYSIS OF LITHIUM CARBIDE WHICH IS PRODUCED BY THE FOLLOWING REACTION: 10 LI + 2 CO2 _ LI2C2 + 4 LI2O IN OUR EXPERIENCE, THE YIELDS OF THIS REACTION WERE QUITE VARIABLE (20-70%). THE VARIABILITY IN YIELD DEPENDED ON THE RATE OF CO2 ADDITION TO THE MOLTEN LITHIUM. THIS YEAR WE REDESIGNED THE ACETYLENE REACTOR TO INCORPORATE AN AUTOMATIC AND VERY SLOW METHOD FOR THE ADDITION OF THE CO2. USING A MASS FLOW CONTROLLER WE NOW ADD ONE MOLE CO2 AT A CONSTANT RATE OVER 60 HOURS. THE ISOTOPIC YIELD OF THIS REACTION IS NOW CONSTANT AND >90%. BASED ON THE SUCCESS OF OUR ACETYLENE REACTION, WE HAVE ALSO STARTED TO REDESIGN THE CYANIDE SYNTHESIS REACTOR TO INCORPORATE MASS FLOW CONTROLLERS.